Recently, with the development of a semiconductor industry, thinning, down-sizing, and weight-reduction of electronic instruments proceeds, and it has been desired to mount electric circuit parts at a high density. In particular, various functional parts contained in OA instruments show a tendency of down-sizing. The correspondence to such a down-sizing has been conventionally realized by miniaturizing various parts being mounted on the surface (thickness direction).
However, in such a conventional correspondence, the mounted area can be small-sized but the total thickness of the mounted parts is increased with repeated application of surface mounting. Thus, in the technical field of surface mounting, the development of the technique capable of attaining thinning has been desired.